With a conventional electrophotographic printer, a charging device charges the surface of a photoconductive drum or belt and an exposing unit such as an LED head writes an electrostatic latent image on the charged surface of the photoconductive drum. The electrostatic latent image is developed with toner into a toner image, which is subsequently transferred to a print medium. The toner image on the print medium is then permanently fixed onto the print medium by a fixing unit.
In the electrophotographic art multi-colour printers are known that produce a plurality of colour toner images on a photoconductive drum or endless belt wherefrom the toner images are transferred directly onto printing stock material such as a paper sheet or paper web material. In an alternative embodiment the toner images formed on a photoconductive recording member are transferred subsequently to an intermediate insulating belt from distinct image forming stations and are then transferred simultaneously to a receiving sheet or web. The multicolour toner image on the print medium is then permanently fixed by a fixing unit into a colour copy or colour print.
Different methods and apparatuses are used for fusing toner images. Non-contact fusing relies on convection of a heated gas such as air or exposure to electromagnetic radiation to soften the toner resins to such an extent that the molten toner particles start to flow and adhere to each other and to the print medium. Non-contact fusing systems are popular for printing on an endless web of print medium (30).
Contact fusing methods as in FIG. 1 use a combination of heat and pressure to melt the toner image onto the print medium as the print medium (30) with the unfused toner image (31) passes trough a pressure contact area between a pair of rollers (10) and (13) wherein at least one roller has a heating source (12). Contact fusing can be used with print media in the form of sheets as well as in the form of an endless web as represented in FIG. 3.
The internal heating system (12) can be assisted by one or more external heating rollers as described in U.S. Pat. No. 6,411,785 and U.S. Pat. No. 6,890,657.
In an alternative transfuse architecture toner images formed on a photoconductive recording member are transferred subsequently to an intermediate insulating belt from distinct image forming stations and are then transferred simultaneously to a heated belt or drum. In the final transfer the molten toner image is transferred from the transfuse belt or drum to the final medium in a contact area by means of a tacky pressure transfer.
The more common configuration is where a multicolour unfused toner image, transferred to the print medium in a previous step is permanently fixed by a fixing unit into a colour copy or colour print as a separate step.
At least one of the rollers (10), (13) contacts a side of the print medium (30) carrying unfused toner images (31). In FIG. 1A the upper roller (10) is the heated fuser roller equipped with an internal heater (12). In the case of a system as in FIG. 1A, which we will further refer to as a simplex fusing system, only roller (10) contacts an unfused image that needs to be fused and is referred to as a fusing roller and the opposing roller (13) is referred to as a pressure roller. For this roller heating is optional. The fuser roller (10) and/or the pressure roller (13) can be replaced by a belt that is guided over 2 or more guiding rollers.
Fuser systems as in FIG. 1A typically fix the toner images on duplex copies in two passes. The print medium (30) with already fused first image (32) as obtained after the fusing of FIG. 1A can be fed a second time into the print system for generating an additional unfused image (131) on the reverse side of the print medium (30) for subsequent fusing as shown in FIG. 1B.
Simultaneous duplex printing systems as in FIG. 1C provide unfused toner images (31),(131) on both sides of a print medium (30) for single pass fusing in the pressure contact area between a pair of fusing rollers (10) and (110) which typically both comprise heaters (12) and (112) and optional additional external heaters. U.S. Pat. No. 6,002,894 describes amongst others such simultaneous duplex fuser embodiments.
Fuser rollers and belts, pressure rollers and belts and transfuse rollers or belts typically comprise one or more elastomer or polymer layers bonded on a mechanically stable belt or cylinder by optional bonding agents. Intermediate layers are typically chosen in function of thermal conductivity and conformance. The outer surface of the fusing surface (14) is typically a high release material and selected from material groups such as silicone resins, fluoropolymers, fluoroelastomers and hybrid compositions thereof comprising a number of proprietary additives and fillers to achieve targeted properties. U.S. Pat. No. 6,365,279 describes an example of a silicone based composition used as an outer layer of a fusing roll or belt.
In most applications of both a fusing roller or belt or transfuse roller or belt, a release agent or parting agent, most frequently a silicone oil, is applied to the fusing roller or belt or transfusing roller or belt to prevent offset (i.e. toner particles adhering to the surface of the fuser roller or belt or transfusing roller or belt instead of to the print medium surface) and to enhance the lifetime or the surface (14) of the fusing roller or belt or transfusing roller or belt
Release agent application systems (29) typically comprise a number of release agent transfer rollers represented in FIG. 2 A. U.S. Pat. No. 5,987,293 describes a typical multiroller oiling system for controlled transfer of a thin layer of release agent to the fuser surface (14).
For the removal of debris and toner contaminants from the fuser roller, fuser surface cleaning systems have been proposed. FIG. 2 shows a prior art type web based cleaning system comprising a supply spool (20) of cleaning web (27) a sponge type pressing roller (25) for pressing the web (21) towards the fusing surface (14) and a take-up spool (22). These webs are typically non-woven polyester/Aramid fibre webs that do not contain any significant amounts of release agent prior to being used. Use of such webs in the function of cleaning the surface by direct contact with the fuser surface (14) has been described in U.S. Pat. No. 5,420,679, U.S. Pat. No. 6,876,832, and U.S. Pat. No. 6,411,785. Use of a similar web immersed in release agent (21) as a release agent supply means in direct contact with the fusing surface (14) as shown in FIG. 2 B has been proposed in U.S. Pat. No. 5,045,890. The web (21) is advanced at a speed of centimeters per minute whereas the surface rotation speed of the fuser surface (14) is typically in the range from 10 to 50 cm/s.
Systems as in FIG. 2 B have the drawback that the nearly stationary web (21) scratches and wears out the fusing surface (14). The nearly stationary web may accumulate contaminants such as paper debris that remain trapped and stationary in the contact area with the fusing surface of the rotating fuser roller or fusing or transfusing belt, and cause local abrasion that degrades the fusing surface. To reduces this type of wear, the use of advanced materials such as PTFE for the fibres of the web have been proposed for the web (21) to reduce the rate of damage to the fusing surface (14). Moreover debris and toner contaminants may still degrade the fuser surface (14) and such contaminants trapped between the web (21) and the fusing surface (14) interfere with the uniform release agent delivery giving rise to visible streaks of release agent on the final print that affect the uniformity of the gloss of the print as discussed in U.S. Pat. No. 6,449,455.
There remains a need for a fuser surface conditioning system that                implements the function of cleaning paper debris and toner contaminants        implements a release agent application function capable of uniform application of small amounts of release agent        is more compact than prior art systems with separated functions of release agent application and fuser surface cleaning        is convenient in terms of reducing the amount of user replaceable fluids and or webs.        avoids maintenance and service issues associated with circulating release agent fluids        further reduce the wear of the fuser surface by avoiding direct contact of the fuser surface with stationary or nearly stationary cleaning means.        